This invention relates to a method and means for performing heat sealing operations.
The heat sealing of a pair of webs containing thermoplastics material by a pair of clamping jaws, at least one of which is heated, is a well known technique. It is also known to employ threads made of a thermoplastics material which are heated while being pressed into place to secure them by adhesion of the softened material.
While both these processes have been practised successfully in themselves, problems can arise if it is required to secure a thread in place on a heat-sealed seam. The thermoplastic thread if melted may shrink away from the heat sealing device and so be attached, at best, only insecurely. If this does not happen, it may stick to the heating device in contact with it, again giving an insecure attachment but also contaminating the apparatus. The use of threads made of a mixture of thermoplastic and non-thermoplastic materials might avoid these problems but it is found they cannot in any case adhere securely by heat to a paper web.